1. Field of the Invention
The present invention relates to a method and apparatus for monitoring a power failure in an apparatus containing at least one functional unit which executes a predetermined function, by monitoring the power failure in at least one function executing section contained in each functional unit, and for restoring the functional unit.
2. Description of the Related Art
FIG. 1 illustrates a relationship between an apparatus and a functional unit. For example, to provide a variety of communication service functions, transmission equipment operating as a node in a communication network includes at least one of functional unit 910-1 through 910-n to provide a variety of functions and a monitoring control unit 920 for monitoring and controlling the at least one of functional unit 910-1 through 910-n. The monitoring control unit 920 and functional units 910 are interchangeable in structure with each other to provide flexibly various functions.
FIG. 2 illustrates an example of a functional unit in a known apparatus. The functional unit 910 in the apparatus includes a primary power monitor 911, an on-board power supply 912 (for generating secondary power from primary power), a secondary power monitor 913 (for monitoring a secondary power voltage and generating a reset control signal), and a function executing circuit 914 (for example, an integrated circuit) for executing a function of the functional unit.
The monitoring control unit 920 in the apparatus includes a primary power monitor 921, an on-board power supply 922 (for generating secondary power 32 from primary power 30), a secondary power monitor 923 (for monitoring a secondary power voltage and generating a reset control signal 42), and a monitoring control processor 924 (for executing a monitoring control function to the functional unit 910). The monitoring control unit 920 and the functional unit 910 are supplied with the primary power 30 (DC-48V, for example) directly from a power facility.
When the primary power 30 is supplied from the power facility, the functional unit 910 monitors the voltage of the primary power 30. When the voltage of the primary power 30 reaches a voltage defined by each functional unit 910, the on-board power supply 912 generates the secondary power 31, and supplies the secondary power 31 to the function executing circuit 914 and the secondary power monitor 913. The secondary power monitor 913 monitors the voltage of the secondary power 31. If the secondary power 31 is not normal, the secondary power monitor 913 activates the reset control signal 41 (ON-state) and outputs the reset control signal 41 to the function executing circuit 914 until the voltage of the secondary power 31 becomes normal. Upon receiving the activated reset control signal 41, the function executing circuit 914 sets the internal circuit thereof to an initial state. When the power is restored, the secondary power monitor 913 deactivates the reset control signal 41 (into a reset release signal), and outputs the reset release signal to the function executing circuit 914.
After the reset control signal 41 is deactivated (reset released), the function executing circuit 914 in the functional unit 910 performs an initial setting process in response to a control signal 43 from the monitoring control unit 920, thereby becoming operative.
If the apparatus includes a plurality of functional units, the apparatus becomes operative after the initial setting process has been performed on all functional units required for the operation of the apparatus.
The monitoring control unit 920 monitors the voltage of the primary power 30 to restore a normal operating condition after an occurrence of power failures including a power interruption, an instantaneous voltage drop, a voltage drop, etc. in the primary power 30 supplied to each of the functional unit 910 and the monitoring control unit 920 from the power facility. At the timing the voltage of the primary power 30 is restored to a predetermined voltage or higher, the monitoring control unit 920 performs the initial setting process on the functional unit 910 by sending the control signal 43 and renders the functional unit 910 operative. The monitoring control unit 920 thus restores the functional unit 910 to the operative state from a shutdown state due to a temporary failure in the primary power 30.
Japanese Unexamined Patent Application Publication No. 02-105654 discloses a technique relating to an initial setting at a startup of a communication apparatus.
The known apparatus including at least one functional unit has drawbacks described below. If a temporary power shutdown or voltage drop takes place in the power facility, a power interruption in the primary power side or the second power side can escape detection because of the following reasons depending on duration of the power interruption, and a voltage value and duration of instantaneous voltage drop.
(1) A primary power voltage monitoring circuit is unable to detect a power shutdown or an instantaneous voltage drop because the duration of the power shutdown or duration of the voltage drop is shorter than detection limits of the circuit.
(2) Power is not interrupted because the voltage of each unit does not sufficiently drops in response to the power shutdown or the instantaneous voltage drop because of electric capacitance of each unit.
(3) Depending on the electric capacitance of each unit, the secondary power voltage drops only in part of the functional unit 910 in response to the power shutdown or the instantaneous voltage drop. Although a monitoring circuit for the secondary power voltage does not detect the power shutdown, part of IC becomes inoperative (in a reset state) due the power voltage drop.
The above cases (1) and (2) are not overcome by setting a threshold in a monitoring voltage. Since each unit is subject to variations in performance, a startup order cannot be determined. Even if a monitoring control unit fails to detect a power shutdown in the primary power, each functional unit may detect the power shutdown in the primary power. The unit suffering from the primary power shutdown also stops outputting the secondary power voltage. A secondary power monitoring circuit detects an abnormal state, and sends a reset control signal to each function executing circuit (IC or the like), thereby setting each circuit to an initial state.
If the primary power is not interrupted in the monitoring control unit 920 but is shut down only in the functional unit 910 in the case of the causes (1) and (2), each function executing circuit 914 remains reset. The initial setting process is performed on the functional unit 910 for operation only if the monitoring control unit 920 gives an instruction.
However, the monitoring control unit 920 with the primary power in normal state is unable to detect the failure taking place in the functional unit 910. So, the functional unit 910 remains inoperative instead of shifting to be operative. If the functional unit 910 continuously remains inoperative, the monitoring control unit 920 fails to learn what happens in the functional unit 910. As a result, although the functional unit 910 is simply inoperative due to the temporary power interruption, the monitoring control unit 920 may determine that the functional unit 910 is faulty.
In the apparatus including a plurality of functional units 910, one of the power failures (1) and (2) may occur, causing the primary power to be shut down in the monitoring control unit 920. In that case, after restoring from the primary power shut down state, the monitoring control unit 920 performs an initial setting process to each functional unit 910 for normal operation. A reference clock may be supplied to each of the plurality of functional units 910 among which an initial setting order is defined. In such a case, the initial setting process must be performed on the plurality of functional units 910 in the defined order. If the primary power is shut down in only the functional unit 910 that requires the initial setting first, the initial setting process is performed only on the functional unit 910 requiring the initial setting first, while a functional unit 910 requiring the initial setting later has already undergone the initial setting process and remains operative. This does not follow the initial setting order. As a result, the apparatus as a whole becomes inoperative.
In the case of the failure (3), the initial setting process for shifting to an operative state is performed on some of function executing circuits 914 included in the functional unit 910, and the monitoring control unit 920 cannot learn what happens in the functional unit 910. In this case, as well, the initial setting process for shifting to an operative state is not performed appropriately. As a result, although the functional unit 910 is in a temporary power failure, the monitoring control unit 920 may determine that the functional unit 910 is faulty.